Friday, November 09, 2012

Haven't you lay awake at night wondering if 36 voxels in your rostromedial prefrontal cortex (RMPFC) can predict your future romantic decisions? If you have, you're in luck. Cooper and colleagues (2012) conducted an fMRI study to answer this burning question in the affirmative.

"and then I asked him with my eyes to ask again yes and then he
asked me would I yes to say yes my mountain flower and first I put my
arms around him yes and drew him down to me so he could feel my breasts
all perfume yes and his heart was going like mad and yes I said yes I
will Yes."

This might be hard for me, but I'll try to seriously convey the major point of the study: how does the brain form first impressions of potential romantic partners? My immediate retort to the experimental approach is why would you ever think that 36 voxels in one brain area (and 34 in another) can drive such a complicated decision??

But that was the finding of this paper, which was published in the Journal of Neuroscience.

To describe the methods in brief, 39 single young heterosexual adults participated in a scanning session where they viewed photographs of their potential dates and rated them on on three dimensions:

a “first-impression”(FI) rating with the scale “How much would you
like to date this person?,” as well as separate ratings of physical
attractiveness (Att) and likability (Like).

After scanning, the same photos were rated again on scales that assessed potential romantic desirability: “How physically attractive is this person?” and “How much do you think you would like this person?” Another 112 young adults also participated in the behavioral part of the study, but not the fMRI part.

For analysis, the authors estimated four models:

Basic decision, two predictors: partners who were later pursued and those who were rejected.

Similar but controlled for reaction time (RT) to the FI decision. This will become important, as we'll see below.

Regions that correlated with subjective desirability ratings: single predictor for all partners with two parametric modulators: one for subjective physical attractiveness (Att) and one for subjective likeability (Like).

Adjustment for partner and relationship effects: single predictor for all partners with two parametric modulators: one for the consensus judgment (hot or not) and one for individual preference (idiosyncratic choice).

Let's look at the results for the basic decision (A) and for subjective attractiveness (B) in the figure below.

Modified from Fig. 2 (Cooper et al., 2012). Neural predictors of subsequent decision compared with areas mediating judgments of physical attractiveness. A,
Brain regions showing greater responses at the time of first viewing
for faces of individuals that are subsequently selected as a potential romantic partner, compared with those who were not. Paracingulate cortex (circled) is the only activated region that significantly independently correlates with subsequent decision in a multiple regression including all activated regions. B, Brain regions positively correlating with subjective ratings of physical attractiveness for each partner. C, Overlap between brain regions related to decision and those related to attractiveness, showing substantial overlap between these variables in the paracingulate cortex. All images thresholded at p < 0.001 voxelwise with extent threshold set to control whole-brain FWE at p < 0.05. Color bars indicate t statistic.

The circled area (A) is called paracingulate cortex by these authors and dorsal anterior cingulate cortex (ACC) by many others. The paracingulate is the only region that correlated with subsequent dating decisions. However, the dorsal ACC is activated in a whole host of situations (Botvinick, 2007; Posner et al., 2007). An explanation for this is well beyond the scope of a single blog post. The big blob (B) correlated with physical attractiveness, and (C) shows the overlap between these two.

It was important to control for the RT of first impression decisions because activity in the ACC is sensitive to "time on task," or how long it takes to process or respond to a stimulus. This means that the ACC shows greater activity when RTs are long. This is a confound for many studies that examine response conflict, or interference, like the well-known Stroop task (RED, BLUE, etc.). If you control for longer RTs that are inevitable in tasks like the Stroop, the interference effect in the ACC goes away (Carp et al., 2010). Hence, the paracingulate could merely be responsive to making dating decisions that are sometimes ambiguous or difficult.

The table below shows that wasn't entirely the case, but the magnitude of the paracingulate activation was diminished when RT was controlled. This wasn't true of two other brain regions (ventral visual cortex, medial precuneus), which weren't even discussed in the paper.

As a final comparison, let's look at activations sensitive to universal hotness vs. idiosyncratic choice. Our friend the paracingulate responded to objective attractiveness, as judged by the entire group of participants. In contrast, another region — 36 voxels in the rostromedial prefrontal cortex — responded to whether the potential partner was desirable to a specific participant.

Overall, the authors have tried to convince us that neural activity in two small regions of the brain mediate first impressions and can predict whether or not we'll pursue contact with a potential romantic partner at a speed dating event. Somehow I think we're missing something here... namely how these medial PFC regions interact with the rest of the brain while making these snap decisions. Not to mention how this intersects with our past experience and future goals.

2 Comments:

It makes sense that people would pay more attention to faces they liked the look of, so I can well believe that there are neural correlates of attraction but hard to tell, from such a paradigm, if they're specific to it.

Links to this post:

About Me

Born in West Virginia in 1980, The Neurocritic embarked upon a roadtrip across America at the age of thirteen with his mother. She abandoned him when they reached San Francisco and The Neurocritic descended into a spiral of drug abuse and prostitution. At fifteen, The Neurocritic's psychiatrist encouraged him to start writing as a form of therapy.